firebase - How to insert server timestamp in Firestore document using REST?

Question

I want to insert a document using a REST call to Firestore createDocument method. One of the fields is a timestamp field that should be set on the server. With Android SDK it's as simple as annotating a Date field with @ServerTimestamp and keeping it null — now how do I do it in REST?

{
  "fields": {
    "timezoneId": {
      "stringValue": "Europe/London"
    },
    "city": {
      "stringValue": "London"
    },
    "timestamp": {
      "timestampValue": "???"
    }
  }
}

I tried using null, 0, empty string, timestamp — everything fails with an error requiring the standard RFC3339 format (e.g. 2018-01-31T13:50:30.325631Z). Is there any placeholder value I can use, or any way to obtain that timestamp?

Answer 1

Waitting for answers